Closed
Description
I use this macro a lot:
macro_rules! is_match {
($value:expr, $($pattern:pat)|+) => {
match $value {
$($pattern)|+ => true,
_ => false
}
}
}But today’s Nightly broke it (#20563 (comment)) with apparently no fix that don’t involve changing the usage syntax.
error: `$pattern:pat` is followed by `|`, which is not allowed for `pat`
A work around (that I’m going to use) is to use tt:
#[macro_export]
macro_rules! matches {
($expression: expr, $($pattern:tt)+) => {
_tt_as_expr_hack! {
match $expression {
$($pattern)+ => true,
_ => false
}
}
}
}
/// Work around "error: unexpected token: `an interpolated tt`", whatever that means.
#[macro_export]
macro_rules! _tt_as_expr_hack {
($value:expr) => ($value)
}But it’s not great since it allows sneaking another match arm into the macro expansion:
fn foo(arg: &str, flux: i32) {
matches!(arg, "bar" | "baz" => flux> 9000, "fuzz");
}
Therefore, I think think that something like the original macro should be possible to write.